Laser-irradiation method and laser-irradiation device

ABSTRACT

A laser-irradiation method which comprises a process for fabricating a semiconductor device, comprising:  
     a first step of forming a thin film amorphous semiconductor on a substrate having an insulating surface; a second step of modifying the thin film amorphous semiconductor into a crystalline thin film semiconductor by irradiating a pulse-type linear light and/or by applying a heat treatment; a third step of implanting an impurity element which imparts a one conductive type to the crystalline thin film semiconductor; and a fourth step of activating the impurity element by irradiating a pulse-type linear light and/or by applying a heat treatment; wherein the peak value, the peak width at half height, and the threshold width of the laser energy in the second and the fourth steps above are each distributed within a range of approximately ±3% of the standard value. Also claimed is a laser irradiation device which realizes the method above.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for annealing (laserannealing) a thin film semiconductor by irradiating a laser light. Theobjects of laser annealing include to crystallize an amorphous thinfilm, to improve the crystallinity of a crystalline thin film, toactivate impurity elements for imparting conductivity, and the like.

[0003] 2. Description of the Related Art

[0004] In recent years, a technique which comprises forming a thin filmsemiconductor on a glass substrate and then fabricating a thin filmtransistor by using the thus obtained thin film is known. This techniqueis essential for the fabrication of an active matrix liquid crystaldisplay device.

[0005] An active matrix liquid crystal display device comprises pixelelectrodes provided in a matrix-like arrangement and thin filmtransistors provided to each of the pixel electrodes in order to controlthe charge that is input and output from the pixel electrode.

[0006] In fabricating the active matrix liquid crystal display device,several hundred thousand of thin film transistors must be integrated ina matrix-like arrangement.

[0007] Thin film transistors utilizing a crystalline silicon film arecapable of yielding high performance, and are preferred for use in theliquid crystal display device. When a crystalline silicon film is used,in particular, peripheral drive circuits using thin film transistors canbe constructed on the same glass substrate. Thus, an advantageousconstitution, which enables a more compact device at a simplerfabrication process at a lower fabrication cost, etc., can beimplemented.

[0008] However, an active matrix liquid crystal device at present hasproblems of causing uneven display or forming stripe patterns in thedisplay. Especially, the stripe patterns are particular in a liquidcrystal display device fabricated through a laser annealing process, andthey considerably impair the visual appearance of the displayed image.

[0009] The stripe patterns differ from point defects and line defects inthat they become visually perceptible depending on the drive conditionsof the liquid crystal display device. Thus, the present inventorsassumed that this phenomena differs from the permanent defectsattributed to, for example, the destruction of thin film transistors andthe formation of short circuit in the wirings and the like.

[0010] Then, as a result of analyzing the liquid crystal display devicefrom various viewpoints, it has been found that the fluctuation in ONcurrent (the current which generates in selecting a pixel electrode)greatly influences the generation of stripe patterns.

[0011] For instance, when a thin film transistor is selected in anactive matrix liquid crystal display device, an ON current generatesbetween the source region (connected to a data line) and the drainregion (connected to a pixel electrode) of the active layer as torealize a particular state (charged state) in which a certain voltage isapplied to the liquid crystal.

[0012] Thus, in case the ON current is extremely small, a problem mayhappen that the charge is insufficient for a pixel electrode. In such acase where the saturated charge is not attained, it becomes impossibleto realize the desired grayscale display, and those pixel regions withinsufficient display are observed as stripe patterns.

[0013] Furthermore, there occurs a phenomenon of causing slight drop inthe voltage written in the pixel electrode immediately after a thin filmtransistor is switched from an ON state to an OFF state (or from an OFFstate to an ON state). The fluctuation in voltage is called as-a “fieldthrough voltage”.

[0014] The field through voltage is another factor causing stripepatterns, because the charge stored in the pixel electrode also changeswith the field through voltage.

[0015] However, in general, the field through current is relaxed by acompensation current which generates between the source/drain(hereinafter referred to as “a field-through compensation current”). Thefield-through compensation current is a current that generates within ashort period of time in switching the thin film transistor from an ONstate to an OFF state (or reverse).

[0016] The present inventors analyzed the trial-fabricated thin filmtransistor, and as a result, it has been found that, with increasing ONcurrent, the field-through compensation current increases, i.e., thatthe field-through voltage becomes more relaxed.

[0017] The analyzed results above can be summarized as follows. That is,the long-unsolved problem of the generation of stripe patterns in aliquid crystal display device is attributed to the fluctuation in ONcurrent of a thin film transistor, and the best solution of the problemis to overcome the fluctuation in ON current.

[0018] Furthermore, the present inventors simulated the generation ofstripe patterns ascribed to insufficient charging described above bymeans of simulation. The simulation was performed by calculating thetime necessary for charging 99.6% or more of the pixel capacitance ofabout 0.2 pF (a total capacitance of a capacitance of the liquidcrystals and the auxiliary capacitance).

[0019] Based on the fact that the fly-back time in VGA is 5 μs, andincluding margin, the results were evaluated by judging whether thepixel capacitance can be charged in a period of 2 μs or not.

[0020] As a result, it was confirmed that an ON current (at a drainvoltage Vd=14 V and a gate voltage Vg=10 V) of 3 μA or higher isnecessary in case of a thin film transistor with a threshold voltage ofabout 2 V.

[0021] In the light of the aforementioned circumstances, the presentinventors came to a conclusion that it is necessary and indispensable toimprove the crystallinity of the semiconductor layer (i.e., thecrystalline silicon film in this case) which greatly influences the ONcurrent above.

[0022] The crystalline silicon film above can be obtained bycrystallizing an amorphous silicon film by applying heat treatment,irradiating a laser light, or by utilizing the both. In particular, themethod of using laser light (said method hereinafter referred to as“laser crystallization”) as a crystallizing means or as a means forimproving the crystallinity is effective from the viewpoint that itenables a crystalline silicon film having excellent crystallinity at alow temperature.

[0023] This method of forming a crystalline silicon film at a lowtemperature is advantageous in that a high performance thin filmtransistor can be fabricated on an inexpensive glass substrate.Accordingly, this method is surely a promising means forcrystallization.

[0024] A pulse-emitting excimer laser is most frequently used in themethod utilizing a laser light irradiation. The method using an excimerlaser comprises emitting a laser having a wavelength in the ultravioletregion by applying a high frequency discharge to a predetermined type ofgas and thereby realizing a particular excitation state.

[0025] In case of forming a crystalline silicon film by irradiating alaser light, however, there is a problem that not always goodreproducibility is obtained on the crystallinity of the resultingcrystalline silicon film. This is due to the influence of the parametersincluded in the process steps from the formation of a silicon film tothe completion of laser annealing treatment.

[0026] The parameters included in the process steps are factorsinfluencing the laser crystallization, and are uncertain factorsinfluencing the crystallinity. They include indirect factors such as thefilm thickness of the amorphous silicon film and the direct ones such asthe irradiation energy of the laser.

[0027] In case of an excimer laser, for instance, the presence offluctuation in the irradiation energy per pulse of the emitted laserlight is found as a problem. Furthermore, the fluctuation in theirradiation energy of the laser and the scattering in energydistribution in the superposed emissions of laser light are known toinduce non-uniform crystallinity.

[0028] For example, the inventors use a laser device in which the laseris linearly beam-processed to provide laser-irradiated surfaces that aresuperposed on each other. Accordingly, the heterogeneity in energydistribution directly induces the fluctuation in ON current as to formtransverse stripe pattern in the image display region.

[0029] As described in the foregoing, the stripe patterns provide afatal problem in manufacturing a commercially feasible liquid crystaldisplay device. Thus, early solution to the problem is keenly demanded.However, by employing the laser device at the present level oftechnology, it is almost impossible to form a crystalline silicon filmhaving a crystallinity which induces perfectly no fluctuation in ONcurrent, which is the cause of stripe patterns.

[0030] In other words, this problem is the rate-determining factor inthe evolution of liquid crystal display device utilizing the lowtemperature polysilicon technique based on laser crystallizationtechnique.

SUMMARY OF THE INVENTION

[0031] An object of the present invention is to provide a technique toovercome the aforementioned problems, which is capable of performinglaser annealing with excellent uniformity and reproducibility, and toprovide a device for implementing the technique. It is also an object ofthe present invention to provide, by applying the technique above, atechnique for fabricating a liquid crystal display device capable offorming an image with high quality and free of stripe patterns.

[0032] According to one aspect of the present invention, there isprovided a laser-irradiation method which comprises a process forfabricating a semiconductor device, comprising:

[0033] a first step of forming a thin film amorphous semiconductor on asubstrate having an insulating surface;

[0034] a second step of modifying the thin film amorphous silicon into acrystalline thin film semiconductor by irradiating a laser light and/orby applying a heat treatment;

[0035] a third step of implanting an impurity element which imparts asingle conductive type to the crystalline thin film semiconductor; and

[0036] a fourth step of activating the impurity element by irradiating alaser light and/or by applying a heat treatment;

[0037] wherein the peak value, the peak width at half height, and thethreshold width of the laser energy in the second and the fourth stepsabove are each distributed within a range of approximately ±3% of thestandard value.

[0038] In the light of the aforementioned problems of conventionaltechniques, the present inventors assumed that the non-uniformity incrystallinity becomes apparent as a result of the mixing of a pluralityof uncertain factors such as the aforementioned thickness of theamorphous silicon film, etc.

[0039] Accordingly, the principal object of the present invention is tosuppress and minimize the fluctuation in the parameters encountered inthe process steps which directly or indirectly influence the lasercrystallization process. Furthermore, another object is to eliminate theuncertain factors as much as possible, while suppressing the fluctuationin the parameters.

[0040] Referring to FIG. 1, for instance, in the fabrication of acrystalline silicon film by irradiating a pulse-emitted linear laserlight, there is observed a fluctuation in the irradiation energy of thelaser light (i.e., the fluctuation in irradiation energy with respect tothe time of irradiation).

[0041] The data shown in FIG. 1 illustrates the fluctuation in the laseroutput (the laser energy or the irradiation energy) per pulse of theemitted radiation (i.e., the fluctuation in irradiation energy withrespect to the passage in irradiation time). In case an appropriate beamformation is performed by using an optical system, the fluctuationcorresponds to the fluctuation in the density of irradiated energy pershot on the irradiated surface.

[0042] In other words, although the irradiated energy is taken here inthe ordinate, it is also possible to convert it and express it in termsof energy density. The laser output herein shows the peak value (maximumvalue) of the laser energy.

[0043] Referring to FIG. 1, it is to be noticed that the peak values ofthe laser output are distributed roughly within a range of ±3% of 640mJ; i.e., the peak values fall within a range of ±3% of a certainstandard value (optimum value) . In the case of the laser device used bythe inventors, the energy density for an irradiated unit area at a laseroutput of 640 mJ is about 250 mJ/cm².

[0044] According to the study of the present inventors, it is knownthat, when laser annealing is performed with a fluctuation larger thanthe range above, the annealing effect becomes scattered, or theuniformity in the surface becomes impaired.

[0045] Incidentally, in case a higher uniformity must be achieved inlaser annealing, the distribution range in laser output is narrowed towithin ±2%, preferably to within ±1.5%, though this may have the expenseof complicated control and increased cost.

[0046] Accordingly, considering the annealing of a semiconductor filmwith reference to FIG. 1, the fluctuation in laser output per pulseemission is constrained to within ±3%, preferably within ±2%, and morepreferably, within ±1.5%. These constraints are particularly preferablein case of annealing a large area using a linearly emitted light oflaser.

[0047] Further, to eliminate the aforementioned stripe patterns, it isalso required not only to suppress the fluctuation in peak values, butalso to suppress the fluctuation in various parameters related to thecrystallization process, and to remove as much as possible the uncertainfactors in laser crystallization.

[0048] In accordance with another aspect of the present invention, thereis provided a laser-irradiation device for irradiating a laser light toa thin film semiconductor provided on a substrate having an insulatingsurface, comprising:

[0049] means for emitting the laser light;

[0050] a gas processor connected to the means for emitting the laserlight;

[0051] a control unit for controlling the output of the laser light bydetecting a part of the laser light and then feeding back the detectedresult to the means for emitting the laser light;

[0052] optical means for shaping the laser light into a linear beam; and

[0053] means for heating the thin film semiconductor;

[0054] wherein, the peak value, the peak width at half height, and thethreshold width of the laser energy are each distributed within a rangeof approximately ±3% of the standard value.

[0055] Furthermore according to still another aspect of the presentinvention, there is provided a laser-irradiation device for irradiatinga laser light to a thin film semiconductor provided on a substratehaving an insulating surface, comprising:

[0056] means for emitting laser light;

[0057] a gas processor connected to the means for emitting the laserlight;

[0058] a control unit for controlling the output of the laser light bydetecting a part of the laser light and then feeding back the detectedresult to the means for emitting the laser light;

[0059] optical system means for shaping the laser light into a linearbeam;

[0060] means for heating the thin film semiconductor; and

[0061] an auxiliary heating device provided in addition to the means forheating the thin film semiconductor;

[0062] wherein, the peak value, the peak width at half height, and thethreshold width of the laser energy are each distributed within a rangeof approximately ±3% of the standard value.

[0063] Referring to FIG. 7, the laser device employed in the presentinvention is briefly described below. The laser device illustrated inFIG. 7 is necessary for providing a laser energy distributed in a rangeshown in FIG. 1.

[0064] Referring to FIG. 7, the pulsed light emitted from a lasergenerator 702 is processed into a pulse beam having a linear crosssection by using an optical system 706, reflected by a mirror 707, andis irradiated to an object substrate 709 through a quartz window 708into a laser irradiation chamber 701.

[0065] As the light emitted from the laser generator 702, usable areradiations in the ultraviolet region, such as a KrF excimer laser(having a wavelength of 248 nm), an XeCl excimer laser (having awavelength of 308 nm), and fourth harmonics (having a wavelength of 265nm) of a xenon-lamp excited Nd:YAG laser.

[0066] Furthermore, a gas processor 703 is connected to the lasergenerator 702. The gas processor 703 corresponds to an excited gaspurifier for removing halides (i.e., fluorides in case of KrF excimerlaser and chlorides in case of XeCl excimer laser) generated inside thelaser generator 702.

[0067] A half mirror 704 is provided between the laser generator 702 andthe optical system 706 above, so that a part of the laser output istaken out and detected by a control unit 705. The control unit 705controls the discharge power of the laser generator 702 incorrespondence with the fluctuation in the detected laser energy.

[0068] The object substrate 709 is placed on a stage 711 provided on asubstrate support table 710, and is maintained at a predeterminedtemperature (300 to 650° C.) by a heater provided inside the substratesupport table 710. The stage 711 is equipped with a thermocouple 712 sothat the measured result may be feed back immediately to control theheater.

[0069] Furthermore, the laser irradiation chamber 701, whose atmosphereis controllable, is equipped with a vacuum evacuation pump 713 as ameans for reducing pressure and for evacuation. The vacuum evacuationpump 713 is capable of realizing high degree of vacuum, e.g., a turbomolecular pump and a criosorption pump.

[0070] A gas supply pipe 714 connected to an O₂ (oxygen) gas bomb via avalve and a gas supply pipe 715 connected to a He (helium) gas bomb viaa valve are provided as a gas supply means. Preferably, the gas usedherein has a purity of more than 99.99999% (7N).

[0071] In the laser irradiation chamber 701 having the constitutiondescribed above, the substrate support table 710 is moved in a directionmaking a right angle with respect to the linear direction along thelinear laser beam. This constitution allows the laser beam to beirradiated while scanning the upper surface of the object substrate 709.

[0072] A gate valve 717 is provided as an inlet and outlet for chargingand discharging the object substrate 709, and is connected to anexternal substrate transport chamber.

[0073] Referring to FIG. 8, the process for processing the pulsed laserbeam inside the optical system 706 (shown in FIG. 7) is brieflydescribed below.

[0074] Firstly, by using an optical system consisting of optical lenses801 and 802, the laser light emitted from a laser generator is shapedinto a laser light having a predetermined beam shape and a predetermineddistribution of energy density.

[0075] The distribution of energy density in the resulting laser lightis corrected by two homogenizers 803 and 804.

[0076] The homogenizer 803 has a function of correcting the energydensity in the width direction within the finally obtained linearlyshaped beam.

[0077] The homogenizer 804 has a function of correcting the energydensity in the longitudinal direction within the finally obtainedlinearly shaped beam. Because the laser beam is extended in thelongitudinal direction for a length of 10 cm or more, the setting of theoptical parameters of the homogenizer 804 must be carried out with greatcare.

[0078] Optical lenses 805, 806, and 808 are provided to linearly shapethe laser beam. In addition, a mirror 807 is provided.

[0079] In the constitution according to the present examples, 12cylindrical lenses (each having a width of 5 mm) constitute thehomogenizer 804. The incident laser beam is split into approximately 10beams.

[0080] That is, the homogenizer is arranged with a little margin withrespect to the laser light so that the inner ten cylindrical lenses aremainly used.

[0081] In the present example, the finally obtained length of the laserradiation energy in the longitudinal direction of the laser radiation is12 cm.

[0082] By employing the constitution above, the unevenness in energydensity of a linear laser light can be eliminated, and uniform annealingcan be applied to a semiconductor material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0083]FIG. 1 shows the fluctuation in the energy density of theirradiated laser per pulse;

[0084]FIGS. 2A to 2E show the process steps in fabricating a thin filmtransistor;

[0085]FIGS. 3A to 3D show the process steps in forming a crystallinesilicon film;

[0086]FIGS. 4A to 4E show the process steps in fabricating another thinfilm transistor;

[0087]FIG. 5 is a scheme of an active matrix liquid crystal displaydevice;

[0088]FIGS. 6A to 6D show the process steps in fabricating a still otherthin film transistor;

[0089]FIG. 7 shows a scheme of a laser irradiation chamber;

[0090]FIG. 8 shows a scheme of an optical system of a laser device;

[0091]FIG. 9 shows a scheme of a part of a laser device;

[0092]FIG. 10 shows a scheme of a part of another laser device;

[0093]FIG. 11 is a graph showing the relation between the laser energyand the pulse width;

[0094]FIG. 12 shows a scheme of another optical system of a laserdevice; and

[0095]FIG. 13 shows a scheme of a still other optical system of a laserdevice.

DETAILED DESCRIPTION OF THE INVENTION

[0096] In the present invention, the distribution of fluctuation invarious parameters influencing either directly or indirectly the lasercrystallization process in annealing a semiconductor film using apulse-emitting type excimer laser is constrained. In this manner, acrystalline silicon film having high uniformity can be obtained withhigh reproducibility.

[0097] The constitution of the present invention is described in furtherdetail by making reference to the examples below. It should beunderstood, however, that the present invention is not to be construedas being limited thereto.

EXAMPLE 1

[0098] The present example describes a case of fabricating a thin filmtransistor according to the invention disclosed by the presentspecification. FIGS. 2A to 2E show the steps of a process forfabricating a thin film transistor of the present example.

[0099] The step of laser annealing in the present example acceleratesthe crystallization of the amorphous silicon film and the activation ofthe impurity ions implanted in the active layer.

[0100] First, a 2,000-Å-thick silicon oxide film is formed on a glasssubstrate 201 as an underlying film 202 by means of sputtering or plasmaCVD. Particularly, when sputtering method using an artificial quartztarget is employed, the grain diameter of each crystal of crystallinesilicon film formed later increases so as to form an active layer withhigh crystallinity.

[0101] An amorphous silicon film 203 is formed thereafter by means ofplasma CVD or low pressure thermal CVD at a film thickness of from 100to 2,000 Å (preferably from 100 to 1,000 Å, representatively, from 200to 500 Å). The amorphous silicon film 203 has a film thicknessdistributed within a range of ±5%, preferably within a range of ±2.5%,in the surface of the substrate.

[0102] Because the film thickness depends on the total combination ofthe various film deposition conditions such as the gas pressure, thedistance between substrates, etc., there is no universal rule concerningthe means for controlling the film thickness within the surface of thesubstrate. However, for instance, considering the fact that the filmthickness distribution in the edge of an object substrate becomesimpaired due to the influence of the change in gas flow and the like, asusceptor larger than the substrate may be prepared in advance, so thata constitution in which the substrate is fit only within a region havingfavorable film thickness distribution is realized. An amorphous siliconfilm with high uniformity can be readily obtained in this manner.

[0103] The fluctuation in film thickness of the amorphous silicon film203 is not preferred because it is directly related with the fluctuationin the crystallinity of the crystalline silicon film. Accordingly, acrystalline silicon film with high uniformity can be obtained byconstraining the fluctuation in film thickness within the aforementionedrange.

[0104] From the viewpoint of improving the density of the film and thecrystallinity of the crystalline silicon film, the amorphous siliconfilm 203 is preferably formed by means of low pressure thermal CVD.

[0105] In forming the film utilizing low pressure thermal CVD, disilane(Si₂H₆), trisilane (Si₃H₈), etc. is used as a starting gas material. Thefilm formation is performed in a temperature range of from 420 to 500°C. In the present example, a 500-Å-thick amorphous silicon film 203 wasformed at a film formation temperature of 450° C. by using disilane. Toobtain a film with uniform film quality and thickness, the fluctuationin film formation temperature (the temperature within the substratesurface) was controlled so that the fluctuation may fall within a rangeof ±1° C.

[0106] In general, the film formation temperature is maintained by usinga heating means such as a heater, but with increasing size of the objectsubstrate, the use of a sheet-wise system becomes dominant. In such acase, a heating means using lamp annealing is effective in achieving auniformly distributed temperature.

[0107] In both cases of using heater or lamp annealing, a thermocoupleis provided to the stage (inclusive of a susceptor) for supporting thesubstrate, and the measured results are fed back for the temperaturecontrol.

[0108] Thus is obtained a state illustrated in FIG. 2A. Once this stateis obtained, the crystallization step is performed by irradiating laserto the amorphous silicon film 203. The laser crystallization step iscarried out by using a laser device above having a constitutionillustrated in FIG. 7.

[0109] Laser light for use in the present example include an excimerlaser using XeCl, KrF, ArF, etc., as the excitation gases, or a fourthharmonic of an Nd:YAG laser and the like. In the present example,however, a KrF excimer laser (emitting light at a wavelength of 248 nm)is employed. In case the load to the optical system and the lasergenerator should be further minimized, it is effective to use an XeClexcimer laser emitting light at a wavelength of 308 nm longer than thatof KrF excimer laser and therefore having a weaker photon energy.

[0110] Laser annealing is performed under an atmosphere containinghelium. Helium has a low specific heat and excels in heat conductivity.These characteristics are extremely effective in accurately controllingthe substrate temperature.

[0111] In case of performing laser annealing in an atmosphere containingoxygen, the surface roughening of the silicon film can be prevented fromoccurring because the surface of the silicon film is protected by theformation of a naturally oxidized film during processing. Thesuppression of the formation of rough surface is extremely effective incase a thin film transistor is completed, and a favorable MOS interfaceis to be formed.

[0112] Accordingly, by introducing gaseous oxygen and gaseous helium ata ratio of 1:1 through gas supply pipes 714 and 715, laser annealing isperformed under a mixed gas atmosphere containing gaseous oxygen andgaseous helium at a gas pressure in a range of from 1 to 760 Torr.

[0113] Thus, the temperature distribution in the surface of the objectsubstrate can be accurately controlled, and the surface roughening ofthe silicon film can be suppressed to a minimum level.

[0114] In addition, from the viewpoint of avoiding inclusion of animpurity into the film during the irradiation of laser, it isfurthermore preferred to introduce gaseous helium and gaseous oxygenwith a purity level exceeding 7N.

[0115] To maintain the gas purity at a high level, it is also effectiveto circulate the gaseous atmosphere inside the laser irradiation chamber701 during the laser irradiation process. For instance, fresh gas may beintroduced continuously while evacuating used gas, or a gas processorand the like may be installed to constantly purify the gas atmosphere.

[0116] Furthermore, in forming the gaseous atmosphere above, it ispreferred to previously remove C (carbon) and N (nitrogen) elementsinside the laser irradiation chamber 701 as much as possible. Thecompounds of C and N elements, such as NH₃, CO, and CO₂ may be found asfactors having bad influence on semiconductor devices.

[0117] Furthermore, C and N elements may form hard coating such asSiC_(x) or SiN_(x) on the surface of the silicon film, and are suspectedto later induce contact failure in the source/drain regions.

[0118] Thus, it is preferred to introduce gaseous oxygen and gaseoushelium after evacuating the laser irradiation chamber 701 to attain ahigh degree of vacuum of 10⁻⁶ Torr or lower. By thus maintaining theinside of the laser irradiation chamber to a state as clean as possible,the concentration of impurities containing C or N elements in thecomposition may be lowered to a level of 1 ppm or even lower.

[0119] As described in the foregoing, the laser device for use in thepresent example enables a highly clean vacuum state by evacuating thelaser irradiation chamber 701 employing a vacuum evacuation pump capableof realizing high degree of vacuum, e.g., a turbo molecular pump, a cryopump, etc.

[0120] Concerning the laser processing temperature (substratetemperature), the object substrate 709 and the stage 711 supporting thesubstrate are maintained at a temperature range of from 300 to 650° C.by using a built-in heater provided to the substrate support table 710.

[0121] In the present example, the substrate temperature is controlledto fall within a temperature range of 450±5° C. (preferably within ±2°C.). It is important to control the temperature in this range from theviewpoint of achieving uniform crystallinity. According to the study ofthe present inventors, it is confirmed that the crystallinity itself canbe improved by controlling the temperature to fall in the range above.

[0122] The reason why a highly uniform crystallinity is obtained can beexplained as follows. That is, by elevating the substrate temperature,the laser irradiation energy can include some margin. This suppressesthe fluctuation in laser irradiation energy in case a laser device whichbecomes unstable at high output is utilized.

[0123] The temperature control is performed while feeding back the dataacquired by the thermocouple 712 provided to the stage 711. The use ofan atmosphere containing helium furthermore facilitates the control ofthe substrate temperature.

[0124] Because the optimum value of the irradiated laser light energydensity differs depending on the crystallinity of the crystallinesilicon film, the present inventors previously perform experiments todetermine the optimal conditions.

[0125] In the present example, laser light is irradiated at an energydensity of 230 mJ/cm² to crystallize the amorphous silicon film 203. Thelaser light is scanned at a rate of 2.4 mm/s and at a frequency of 40Hz.

[0126] The laser light for use in the present invention is emitted froma pulse-emitting device, and a plurality of pulsed beams are superposedon each other to scan the irradiation plane (the surface of the siliconfilm in this case).

[0127] Referring to FIG. 11, the distribution of laser energy per pulseis described below. In FIG. 11 is shown an ideal waveform per pulse ofthe laser radiation, and the other waveforms are omitted. The pulsewidth is taken in the abscissa at units of time. The laser energy (whichmay expressed in terms of density) is taken in the ordinate at anarbitrary unit.

[0128] In the present invention, the most important key is to preciselycontrol the laser energy, and this control directly influences thecrystallinity of the crystalline silicon film.

[0129] The parameters which require precise control include peak value,peak width at half height, and threshold width. Referring to FIG. 11,the explanation for the parameters is given below.

[0130] Referring to FIG. 11, the peak value E_(max) is the maximum valueof the laser energy. An ideal waveform is shown in FIG. 11, and differsfrom a practical peak. More specifically, in practice, it is found agreat problem that the peak value greatly fluctuates during theirradiation. Such a fluctuation in peak value is found as a fluctuationin energy density of a beam irradiated onto the irradiation surface, andit greatly influences the crystallinity.

[0131] The peak width at half height corresponds to the pulse width(where time is taken for the unit) taken at half height (expressed by½E_(max) of the peak value E_(max). In other words, it corresponds tothe average pulse width in case of performing laser annealing for asingle pulse. Thus, in general, the peak width at half height isdiscussed as the pulse width.

[0132] The threshold width corresponds to the pulse width (where time istaken for the unit) when the laser energy is at the threshold value(also called as a fusion threshold value, expressed herein by E_(th)).The threshold width is a value corresponding to about ¼ to ½ of the peakwidth at half height.

[0133] The threshold value (fusion threshold value) corresponds to thethreshold indicating that any laser energy at this value or higherinitiates the fusion of the irradiated surface (the surface of thesilicon film in this case). Accordingly, within the range of thresholdwidth, laser light is irradiated with an energy sufficient to melt theirradiated surface.

[0134] In the present invention, the range corresponding to thethreshold width as shown in FIG. 11 is denoted as the energy regioneffective for melting a silicon film, i.e., “an effective meltingregion”. Thus, the most important factor in suppressing the fluctuationin laser crystallization energy is to precisely control the effectivemelting region.

[0135] Accordingly, in controlling the effective melting area above, itis indispensable to control the fluctuation of the peak value E_(max),the peak width at half height, and the threshold width. Thus, as isproposed in the present invention, it is the key factor to control thepeak value E_(max), the peak width at half height, and the thresholdwidth within a range of ±3%, preferably within a range of ±1.5% of thetargeted value.

[0136] In the present example, with reference to FIG. 7, the fluctuationin peak value E_(max) is controlled by taking out a part of the laserlight emitted from the laser generator 702 by using the half mirror 704,and based on the energy detected by the control unit 705.

[0137] As described above, it is extremely effective in suppressing thefluctuation in the peak value E_(max) to elevate the substratetemperature and to thereby allow a margin in the laser energy necessaryfor the crystallization.

[0138] Furthermore, the purity of the excitation gas (Kr, F, Xe, Cl,etc.) in the laser generator 702 shown in FIG. 7 becomes extremelyimportant in controlling the peak width at half height and thresholdwidth. If the purity of the excitation gas drops, the emission of laserlight itself fluctuates as to affect the rise of laser pulse.

[0139] For example, gases such as Kr or F are generally diluted with aninert gas such as Ne, and then introduced inside the laser generator702. Accordingly, to prevent fluctuation from occurring in the laserlight, these gases preferably have a purity exceeding 7N.

[0140] Even in case an excitation gas with high purity is used, halidesare formed during the prolonged use thereof, and this is found as thecause of impairing the purity of the gas inside the laser generator 702.

[0141] Accordingly, in the laser device for use in the present example,a gas processor 703 is connected to the laser generator 702 to maintainthe high purity of the excitation gas. The gas processor 703 correspondsto a purifier which captures and removes the aforementioned halides byusing an extremely low-temperature capture medium while circulating theexcitation gas inside the laser generator 702.

[0142] As described in the foregoing, the use of a laser deviceaccording to the present example, whose constitution is shown in FIG. 7,enables controlling the peak value E_(max), the peak width at halfheight, and the threshold width within a range of ±3%, preferably withina range of ±1.5% of the targeted value.

[0143] Precise control of the effective fusion region is possible byprecisely controlling the peak value E_(max), the peak width at halfheight, and the threshold width. That is, a crystalline silicon filmhaving excellent uniformity can be obtained because laser annealing ofthe irradiated surface is performed under a homogeneous laser energy.

[0144] In the present example, laser annealing is applied under theprecise control above on a silicon film at an arbitrary unit area by aduration of from 100 to 5,000 nsec. This period of time is necessary forachieving the required crystallinity, and was obtained experimentally bythe present inventors.

[0145] However, because the present inventors regard only the durationof laser annealing in the effective fusion region as the process time,and regard the cumulative threshold width as the process time. Thus, theprocess time can be expressed by the threshold width t_(n) according tothe following equation 1: $\begin{matrix}{{\sum\limits_{n = 1}^{m}\quad t_{n}} = {100\quad {to}\quad 5,000\left( {n\quad \sec} \right)}} & \left\lbrack \left. {{Equation}\quad 1} \right\rbrack \right.\end{matrix}$

[0146] That is, the cumulative time duration of performing laserannealing in the effective fusion region corresponds to the processtime. For instance, the peak width at half height in case of laserannealing in the present example is in a range of from 30 to 40 nsec,and the threshold width (duration of irradiating laser in the effectivefusion region) is in a range of from 10 to 20 nsec.

[0147] Furthermore, because a linear laser having a lateral width of 0.9mm is scanned at a scanning rate of 2.4 mm/s in such a manner that theirradiated region may be superposed on each other, the pulsed laserirradiation is effected for about 15 times per unit area (that is, m=15in Equation 1 above). Accordingly, in the present example, the durationof irradiating laser in the effective fusion region is in a range offrom 150 to 300 nsec.

[0148] It is also possible to appropriately control the duration oflaser irradiation in the effective fusion region by increasing theirradiation time per unit area by either increasing the frequency ofpulsed laser or by decreasing the scanning rate.

[0149] By thus performing laser annealing, a crystalline silicon film204 as shown in FIG. 2B can be obtained. Because the crystalline siliconfilm 204 is formed by a precisely controlled laser annealing, thesilicon film is obtained with excellent uniformity and reproducibility.

[0150] The term “excellent uniformity” as referred herein signifiesthat, when the silicon film is used in constructing an electro-opticaldevice of an active matrix type, the resulting products are obtainedwith no uneven display or stripe patterns, or with no fluctuation incharacteristics per lot.

[0151] Furthermore, because C and N elements are completely removed fromthe inside of the crystalline silicon film 204, their concentration inthe vicinity of the interface is reduced to 2×10¹⁹ cm⁻³ or lower, andthe concentration inside the bulk is 5×10¹⁸ cm⁻³ or lower.

[0152] The concentration above is obtained from the minimum value ofSIMS (secondary ion mass spectroscopy) analysis. The term “bulk” asreferred herein signifies the inside of the film exclusive of the regionin the vicinity of the interface.

[0153] The thus obtained crystalline silicon film 204 is then patternedto form an island-like semiconductor layer 205 to provide the activelayer of a thin film transistor (FIG. 2C).

[0154] In an embodiment of the present example, an active layer isformed after laser annealing is performed, but laser light may beirradiated after forming the active layer.

[0155] This case comprises annealing a minute area. Accordingly, thedesired effect can be obtained at a lower laser light output. That is,the fluctuation can be further suppressed by taking a margin in laseroutput.

[0156] After obtaining the active layer (island-like semiconductorlayer) 205, a silicon oxide film which functions as a gate insulatingfilm 206 is formed in such a manner that it may cover the active layer205. A 1,000-Å-thick silicon oxide film is formed as the gate insulatingfilm 206 by means of plasma CVD, but a silicon nitride film or a siliconoxynitride film expressed by SiO_(x)N_(y) may be used in the place ofthe silicon oxide film.

[0157] A 3,000-Å-thick aluminum film not shown in the figure is formedto construct a gate electrode 207. Scandium is added at a concentrationof 0.2% by weight into the aluminum film to suppress the generation ofhillocks and whiskers.

[0158] Hillocks and whiskers are needle-like or acicular protrusionsattributed to the abnormal growth of aluminum. Hillocks and whiskers arenot preferred because they induce short circuit between the electrodesor the wirings.

[0159] For the gate electrode 207, it is also possible to useelectrically conductive materials other than aluminum.

[0160] After placing a resist mask not shown in the figure, an aluminumfilm also not shown is patterned by using the mask. In this manner, apattern which provides the base for constituting the gate electrode 207is formed. After forming the pattern for the construction of the gateelectrode 207, an anodic oxide film is formed with the aforementionedresist mask (not shown) being placed.

[0161] In this case, an aqueous solution containing 3% of nitric acid isused as the electrolytic solution. The anodic oxidation step isperformed by applying a current between the patterned aluminum film (notshown) functioning as the anode and a platinum cathode. In this manner,an anodic oxide film 208 is formed on the exposed surface of thepatterned aluminum film.

[0162] The anodic oxide film 208 thus formed is porus. Furthermore,because a resist mask not shown in the figure is present, a porousanodic oxide film 208 is also formed on the sides of the pattern.

[0163] The porous anodic oxide film is formed at a film thickness(distance of growth) of 3,000 Å. An offset gate region can be formeddepending on the film thickness of the porous anodic oxide film 208. Thefilm thickness of the anodic oxide film 208 can be controlled by theduration of anodic oxidation.

[0164] Then, after removing the resist mask not shown, anodic oxidationis performed again. In this step, an ethylene glycol solution containing3% of tartaric acid and neutralized by ammonia is used as theelectrolytic solution.

[0165] Because the electrolytic solution intrudes into the porous anodicoxide film 208 in this step, dense anodic oxide film 209 is obtained ina state as such that the anodic oxide film 209 is in contact with thegate electrode 207.

[0166] The film thickness of the dense anodic oxide film 209 can becontrolled by adjusting the applied voltage. In the present example, a900-Å-thick anodic oxide film 209 is formed.

[0167] An offset gate region can be formed in the later step by thicklyproviding the dense anodic oxide film 209. In such a case, the offsetgate region can be formed depending on the film thickness. In thepresent example, however, the contribution of the film to the formationof an offset gate region is negligible because the anodic oxide film isthin.

[0168] Thus is obtained a state illustrated in FIG. 2C. Referring toFIG. 2C, impurity ions are implanted to form source and drain regions.In this case, P (phosphorus) ions are implanted at a dose of 1×10¹⁵atoms/cm² to fabricate an N-channel type thin film transistor.

[0169] B (boron) ions are implanted for the fabrication of a P-channeltype thin film transistor.

[0170] By implanting impurity ions to the structure illustrated in FIG.2C, impurity ions are implanted into regions 210 and 211. No impurityions are implanted into the regions 212 and 213. Because no voltage isapplied to the regions 212 and 213 by the gate electrode 207, theseregions function as offset gate regions and not as channel formingregions.

[0171] The region 214 functions as a channel forming region. Thus isobtained a state as shown in FIG. 2D.

[0172] Upon completion of the implantation of impurity ions, laser lightis irradiated in order to activate the region doped with the impurityions and to anneal the region damaged by the ion bombardment(hereinafter, this step is referred to as a “laser activation step”).

[0173] Similar to the laser crystallization step, the laser activationstep can be performed to achieve an annealing effect with highuniformity by applying a similar precise control using the same deviceas that used in the laser crystallization. In this step, however, theheating temperature for the object substrate must be determined bytaking the heat resistance of the aluminum gate electrode 207 intoconsideration.

[0174] Accordingly, in the present example, the laser activation step iscarried out while heating the substrate temperature to 200° C. If amaterial having high heat resistance is used for the gate electrode 207,as a matter of course, the temperature of the substrate may be elevatedin accordance with the heat resistance.

[0175] The conditions of laser irradiation in the laser activation stepchange depending on the crystallinity of the active layer 205 as well ason the quantity of implanted impurity ions. Accordingly, optimumconditions must be determined previously by repeatedly conductingexperiments. In the present example, laser irradiation is effected at anenergy density of 160 mJ/cm².

[0176] After obtaining a state illustrated in FIG. 2D, a silicon nitridefilm or a silicon oxide film is formed to provide an interlayerinsulating film 215. A multilayered film of a silicon nitride film and asilicon oxide film may be used for the interlayer insulating film 215.Otherwise, a multilayered film of silicon nitride film and a resin filmcan be used as well.

[0177] After forming an interlayer insulating film 215, contact holesare provided therein. Then, a source electrode 216 and a drain electrode217 are formed. Thus is completed a thin film transistor as shown inFIG. 2E.

[0178] The thin film transistor thus fabricated comprises a highlyuniform active layer for the key portion thereof. Accordingly, a highperformance thin film transistor capable of stable operation can beimplemented.

[0179] The N-channel thin film transistor thus fabricated exhibitsfavorable electric characteristics which yield a threshold value ofabout 1.5 V and an ON current in a range of from 10 to 15 μA under driveconditions with a drain voltage Vd of 14 V and a gate voltage Vg of 10V.

EXAMPLE 2

[0180] The present example refers to a case of crystallizing theamorphous silicon film, which is referred in example 1, by means of heattreatment. In the present example, furthermore, a metallic element isused for the acceleration of crystallization. As a matter of course, thecrystallization may be effected without using a metallic element.

[0181] Thus, an object of the present example is to further improve, byapplying laser annealing, the crystallinity of the crystalline siliconfilm formed by heat treatment.

[0182] Since the process steps other than the crystallization are thesame as the constitution described in example 1, the description in thepresent example is restricted only to the points differing from thosedescribed in example 1 with reference to FIG. 3.

[0183] First, a 2,000-Å-thick silicon oxide film is formed by sputteringor plasma CVD as a base film 302 on a substrate 301.

[0184] Then, an amorphous silicon film 303 is formed to a thickness offrom 200 to 500 Å by means of plasma CVD or low pressure thermal CVD.Similar to example 1, the amorphous silicon film 303 is formed in such amanner that the fluctuation in film thickness on the surface of thesubstrate is constrained to distribute within ±5%, preferably, ±2.5% ofthe targeted value.

[0185] After forming the amorphous silicon film 303, an UV light isirradiated thereto under an oxygen atmosphere to form a very thin oxidefilm (not shown) on the surface of the amorphous silicon film 303. Theoxide film improves the wettability of the surface to a solution that isapplied thereon on the later step of introducing a metallic element bymeans of solution coating (FIG. 3A).

[0186] Then, a metallic element is introduced to accelerate thecrystallization of the amorphous silicon film 303. The details of thistechnique is disclosed in JP-A-Hei 6-232059 and JP-A-Hei 7-321339 (theterm “JP-A-” as referred herein signifies “an unexamined publishedJapanese patent application”) filed by the present inventors.

[0187] In the present example, Ni (nickel) is used as the metallicelement which accelerates the crystallization. In addition to Ni, usablemetallic elements include Fe, Co, Cu, Pd, Pt, and Au.

[0188] In the present example, a nickel acetate solution is used tointroduce metallic Ni. More specifically, a nickel acetate solutionprepared at a predetermined Ni concentration (10 ppm by weight in thepresent case) is applied dropwise to the amorphous silicon film 303. Inthis manner, a state comprising an aqueous film 304 is realized (FIG.3B).

[0189] The solution applied in excess is blown away by means, of spindrying using a spin coater (not shown). Thus, an ultrathin nickel layeris formed on the oxide film (not shown) formed on the amorphous siliconfilm 303 by this solution-coating process.

[0190] A crystalline silicon film 305 is then obtained by performingheat treatment at a temperature in a range of from 500 to 700° C.,representatively, at 600° C., for a duration of 4 hours in an inertatmosphere or in an inert atmosphere containing gaseous hydrogen (FIG.3C).

[0191] It is important to control the temperature during the heattreatment to fall within a range of ±5° C., preferably within ±2° C., ofthe targeted temperature, because the intergranular crystallinity of thecrystalline silicon film depends on this crystallization step effectedby the present heat treatment.

[0192] Similar to example 1, it is necessary to precisely control thetemperature by monitoring the substrate temperature using atemperature-detecting element, such as a thermocouple, provided to thesusceptor which supports the substrate.

[0193] Once the crystalline silicon film 305 is obtained, laser light isirradiated to improve the crystallinity. Similar to the lasercrystallization process described in example 1, the laser annealing mustbe conducted under strictly controlled conditions. Furthermore, as wasthe case in example 1, a laser device whose constitution is shown inFIG. 7 is used in this process.

[0194] The laser annealing step comprises irradiating anultraviolet-emitting laser to the crystalline silicon film. In thismanner, the crystalline silicon film is once molten, and thenrecrystallized to improve the crystallinity.

[0195] As compared with an amorphous silicon film, a crystalline siliconfilm less absorbs light in the ultraviolet wavelength region.Accordingly, laser light for use in the laser annealing step must beirradiated with a higher energy. Furthermore, the laser energy must behigher for a crystalline silicon film having higher crystallinity. Thus,the laser energy must be determined experimentally in advance. In thepresent example, laser is irradiated at an energy density of 260 mJ/cm²(FIG. 3D).

[0196] Thus is obtained a crystalline silicon film 306 whosecrystallinity is considerably improved. Similar to the case in example1, the crystalline silicon film 306 thus obtained yields excellentuniformity with high reproducibility.

EXAMPLE 3

[0197] The present example refers to a case of fabricating a thin filmtransistor comprising an LDD (lightly doped drain) region by means of aprocess described in example 1, but which is further ameliorated.

[0198] First, the same process steps as those described in example 1 arefollowed to obtain an impurity-implanted state shown in FIG. 2D.

[0199] Then, the porous anodic oxide film 208 is removed, and theimpurity ions are implanted again. The implantation of impurity ions iseffected in the same manner and by using the same impurity ions as inthe step of forming the source region 210 and the drain region 211,except for lowering the dose.

[0200] As a result, impurity ions (for instance, P ions) are implantedinto regions 212 and 213 at a density lower than that in the source anddrain regions. In this manner, low density impurity regions are formedin regions 212 and 213. The low density impurity region 213 on the drainregion side 211 becomes the region generally known as LDD (lightly dopeddrain) region.

[0201] Then, once the impurity implanted regions are formed, a laseractivation step similar to that in example 1 is performed. According tothe study of the present inventors, however, it is known that the lowdensity impurity regions (particularly the LDD regions) are apt toreflect the influence of the fluctuation in laser energy.

[0202] Accordingly, the application of laser annealing under precisecontrol in accordance with the present invention is a particularlyeffective means in fabricating a low density impurity region havingexcellent uniformity, as well as in fabricating a thin film transistorhaving uniform electric properties.

[0203] A complete thin film transistor is then obtained by performingthe step illustrated in FIG. 2E.

[0204] The LDD region has the functions similar to that of an offsetgate region. That is, it relaxes the intense electric field between thechannel forming region and the drain region, and decreases the leakcurrent during the OFF operation. Furthermore, in case of an N-channeltype thin film transistor, it suppresses the generation of hot carriers;hence, it prevents the problem of degradation from occurring due to thepresence of hot carriers.

EXAMPLE 4

[0205] The present example refers to a case in which an active matrixliquid crystal display device is constructed by using a thin filmtransistor (TFT) fabricated in accordance with the present invention.The fabrication process for the pixel TFTs provided in the pixel regionand the circuit TFTs provided in the peripheral drive circuit isdescribed briefly below with reference to FIGS. 4A to 4E.

[0206] It should be noted that, however, the description concerning thecontrol on fluctuation and the like of the parameters in the processsteps is omitted, because it is already described in example 1. In thedescription below, the process steps for fabricating circuit TFTs andpixel TFTs are referred by taking it for granted that the basic processis the same as the constitution explained in example 1.

[0207] First, a glass substrate 401, representatively Corning 7059 andthe like, is prepared. As a matter of course, a quartz substrate or asemiconductor material having an insulating surface can be used. Then, asilicon oxide film is formed at a thickness of 2,000 Å to provide anunderlying film 402. The underlying film 402 can be formed by means ofsputtering or plasma CVD.

[0208] A 100 to 1,000-Å-thick amorphous silicon film (not shown) isformed thereon by means of plasma CVD or low pressure thermal CVD. Inthe present example, a 500-Å-thick film is formed by low pressurethermal CVD.

[0209] Then, the amorphous silicon film not shown in the figure iscrystallized by means of a proper crystallization method. Thecrystallization can be performed by a heat treatment in a temperaturerange of from 550 to 650° C. for a duration of 1 to 24 hours, or byirradiating laser at a wavelength of 248, 265, or 308 nm. The bothmethods can be used simultaneously, or an element (such as Ni) whichaccelerates the crystallization may be added.

[0210] Then, the crystalline silicon film thus obtained by crystallizingthe amorphous silicon film is patterned to form island-likesemiconductor layers as active layers 403 and 404.

[0211] A silicon oxynitride film 405 expressed by SiO_(x)N_(y) is formedto a thickness of 1,200 Å by plasma CVD. In the later steps, the siliconoxynitride film 405 functions as a gate insulating film. A silicon oxidefilm or a silicon nitride film can be used in the place of the siliconoxynitride film.

[0212] Then, a 4,000-Å-thick aluminum film 406 is formed by means of DCsputtering. Scandium is added at a concentration of 0.2% by weight intothe aluminum film to suppress the generation of hillocks and whiskers.The aluminum film 406 thus formed functions in the later steps toprovide a gate electrode.

[0213] A film of other metallic materials, such as Mo, Ti, Ta, Cr, etc.,may be used in the place of the aluminum film. Otherwise, a conductivefilm, such as of polysilicon or silicide materials, can be used as well.

[0214] Then, anodic oxidation is performed in an electrolytic solutionusing the aluminum film 406 as an anode. An ethylene glycol solutioncontaining 3% of tartaric acid neutralized by aqueous ammonia to adjustthe pH value thereof to 6.92 may be used for the electrolytic solution.This process is effected by using platinum as a cathode and by applyinga chemical conversion current of 5 mA at a final voltage of 10 V.

[0215] The thus obtained not shown dense anodic oxide film is effectiveto later improve the adhesiveness to the photoresist. Furthermore, thefilm thickness can be controlled by changing the duration of appliedvoltage (FIG. 4A).

[0216] Then, after thus obtaining the state shown in FIG. 4A, thealuminum film 406 is patterned to form the prototype for the gateelectrode that is formed in a later step. Then, a second anodicoxidation is performed to form anodic oxide films 407 and 408 (FIG. 4B).

[0217] The second anodic oxidation is effected in an aqueous 3% oxalicacid provided as the electrolytic solution, and by using a platinumcathode under a chemical conversion current of from 2 to 3 mA and at afinal voltage of 8 V.

[0218] In this step, the anodic oxidation proceeds in a directionparallel to the base. Furthermore, the length of the porous anodic oxidefilms 407 and 408 is controlled by changing the duration of appliedvoltage.

[0219] Then, after removing the photoresist by using a proper strippingsolution, a third anodic oxidation is performed. An ethylene glycolsolution containing 3% of tartaric acid neutralized by aqueous ammoniato adjust the pH value thereof to 6.92 may be used for the electrolyticsolution. This process is effected by using platinum as the cathode andby applying a chemical conversion current of 5 to 6 mA at a finalvoltage of 100 V.

[0220] The anodic oxide films 409 and 410 thus obtained are extremelydense and strong. Accordingly, they are effective for protecting thegate electrodes 411 and 412 from being damaged in the later steps suchas the doping step. However, because the strong anodic oxide films 409and 410 are sparingly etched, it tends that a longer etching timeduration is taken in forming contact holes. Thus, the anodic oxide filmsare preferably formed at a thickness of 1,000 Å or less.

[0221] After obtaining a state as is shown in FIG. 4B, impurities areimplanted into active layers 403 and 404 by means of ion doping. In caseof fabricating an N-channel TFT, for instance, P (phosphorus) isimplanted, whereas B (boron) is implanted as an impurity in case offabricating a P-channel TFT.

[0222] Thus, source/drain regions 413 and 414 for the circuit TFT aswell as source/drain regions 415 and 416 for the pixel TFT are formed ina self-aligned manner.

[0223] Then, ion implantation is performed again after removing theporous anodic oxide films 407 and 408. In this case, ions are implantedat a dose lower than that at the previous ion implantation.

[0224] Low density impurity regions 417 and 418 for the circuit TFT, achannel forming region 421, low density impurity regions 419 and 420 forthe pixel TFT, and a channel forming region 422 are formed in aself-aligned manner.

[0225] Once a state illustrated in FIG. 4C is obtained, KrF laser isirradiated and thermal annealing is performed. In the present example,laser light is applied at an energy density of from 160 to 170 mJ/cm²,and thermal annealing is effected at a temperature in a range of from300 to 450° C. for a duration of 1 hour. The crystallinity of the activelayers 403 and 404, which were damaged in the ion doping step, can beimproved by performing this step.

[0226] A silicon nitride film (which may be replaced by a silicon oxidefilm) is formed by means of plasma CVD at a thickness of from 3,000 to5,000 Å to provide a first interlayer insulating film 423. Theinterlayer insulating film 423 may have a multilayered structure (FIG.4D).

[0227] After the first interlayer insulating film 423 is formed, theinterlayer insulating film provided on the source region 413, the gateelectrode 411, and the drain region 414 of the circuit TFT, as well asthe source region 415 of the pixel TFT is etched to form contact holes.

[0228] Then, a source electrode 424, a gate electrode 425, and a drainelectrode 426 for the circuit TFT as well as the source electrode 427for the pixel TFT are formed by using a layered film of titanium and amaterial containing aluminum as a principal component.

[0229] Then, a silicon nitride film (which may be replaced by a siliconoxide film) is formed by means of plasma CVD at a thickness of from3,000 to 5,000 Å to provide a second interlayer insulating film 428. Theinterlayer insulating film 428 may have a multilayered structure (FIG.4E).

[0230] After forming the second interlayer insulating film 428, theinterlayer insulating films 428 and 423 provided on the drain region 416of the pixel TFT are etched to form contact holes, and to thereby form apixel electrode 429 comprising a transparent electrically conductivefilm. In this manner, a circuit TFT and a pixel TFT are formed asillustrated in FIG. 4E.

[0231] A scheme of the active matrix liquid crystal display devicecomprising the circuit TFT and the pixel TFT described above is providedin FIG. 5. Referring to FIG. 5, horizontal scanning circuit 502 and avertical scanning circuit 503 are provided on a glass substrate 501.

[0232] An external image signal is taken through an input terminal 504,and is sent to a pixel electrode by using a pixel TFT controlled by thehorizontal and the vertical scanning circuits 502 and 503 as a switchingelement. Then, images are displayed in the pixel region 505 by changingthe electro-optical properties of the liquid crystal being interposedbetween the pixel electrode and the opposing substrate. A commonelectrode 506 for applying a predetermined voltage to the opposingsubstrate is also provided.

[0233] Thus, a circuit TFT as shown in the aforementioned FIGS. 4A to 4Ecan constitute the horizontal and the vertical scanning circuits 502 and503 in a CMOS structure in which N-channel type and P-channel type arecombined in a complementary structure.

[0234] As shown in the enlarged FIG. 507 for the pixel region 505, thepixel TFTs can be placed on each of the cross points of the gate andsource lines provided in a matrix-like arrangement. In this manner, theycan be used as switching elements controlling the quantity of chargeinput and output into the pixel electrode.

[0235] The device shown in FIG. 5 displays the image in a mannerdescribed schematically above, and is a compact and high performancepanel comprising a peripheral circuit operating at an operationfrequency of 3 MHz or higher and yielding a contrast ratio of 100 orhigher at the display portion.

[0236] The active matrix liquid crystal display device described in thepresent example comprises circuit TFTs and pixel TFTs having an activelayer which exhibits crystallinity with excellent uniformity andreproducibility. Accordingly, all the thin film transistors yielduniform characteristics.

[0237] In particular, because the pixel TFTs with uniformcharacteristics are used, no lateral stripe patterns generate indisplaying an image. Accordingly, the constitution of the presentexample is industrially highly advantageous.

EXAMPLE 5

[0238] The constitutions described in the foregoing examples 1 to 4comprise planar type thin film transistors, but the active layeraccording to the present invention can be applied not only to the planartype, but also to all types of thin film transistors.

[0239] Accordingly, the present example refers to a case of fabricating,for instance, a reverse stagger type thin film transistor. Such a typeof thin film transistor can be formed in accordance with the techniquedisclosed in JP-A-Hei5-275452 or JP-A-Hei 7-99317. Thus, the details ofthe conditions, thickness of the films, etc., may be referred to thepublication above.

[0240] In addition, although not explained in particular, the factorsinfluencing laser annealing are controlled in a manner similar to thatdescribed in example 1.

[0241] Referring to FIG. 6A, a gate electrode 602 made of anelectrically conductive material is formed on a substrate 601 having aninsulating surface. Considering the later crystallization of the siliconfilm, the gate electrode 602 is preferably made of a material having ahigh thermal resistance.

[0242] Furthermore, to improve withstand voltage, an anodic oxide filmmay be formed on the surface and the sides of the gate electrode 602 bymeans of a known technique, i.e., anodic oxidation. It is also possibleto implement a constitution comprising an LDD region or an HRD region byutilizing the anodic oxide film thus obtained by the anodic oxidationprocess above. For the details of this technique, reference can be madeto JP-A-7-169974 filed by the present inventors.

[0243] Then, a silicon oxide film which functions as the gate insulatingfilm 603 is formed by means of plasma CVD, and an amorphous silicon film(not shown) is formed thereon by low pressure thermal CVD. The amorphoussilicon film not shown is then crystallized by the means described inexample 1 to provide a crystalline silicon film 604 which constitutes anactive layer (FIG. 6A).

[0244] The thus obtained crystalline silicon film 604 is patterned toform an island-like semiconductor layer which constitutes the activelayer 605.

[0245] A silicon nitride film (not shown) is formed thereafter to coverthe active layer 605. Then, a resist mask (not shown) is provided on thesilicon nitride film, and is patterned by back surface exposure toselectively remove the silicon nitride film by etching.

[0246] The island-like pattern 606 made of silicon nitride film thusobtained functions as a masking material in the later step of ionimplantation.

[0247] Thus is obtained a state illustrated in FIG. 6B. Then, impurityions which render the exposed active layer 605 monoconductive(one-conductive) are implanted. This step can be performed by followinga known ion implantation method. After the ion implantation, theimpurity ions are activated by laser annealing and the like. As a matterof course, the laser annealing is effected in accordance with thepresent invention.

[0248] Thus, a source region 607 and a drain region 608 are formed inthe active layer 605. The region which was not implanted with ions dueto the presence of the island-like pattern 606 becomes a channel-formingregion 609 (FIG. 6C).

[0249] Once the state illustrated in FIG. 6C is obtained, a siliconoxide film 610 is formed as an interlayer insulating film by means ofplasma CVD. Furthermore, contact holes which reach the source region 607and the drain region 608 are formed.

[0250] Thus, by forming a source electrode 611 and a drain electrode 612comprising an electrically conductive material, a reverse stagger typethin film transistor as shown in FIG. 6D is completed.

[0251] As is described above, the present invention can be sufficientlyapplied to a reverse stagger type thin film transistor. Because thereverse stagger type thin film transistor comprises a gate electrode 602being placed on the lower side of the active layer 605, the entireactive layer 605 can be advantageously subjected to a uniform treatmentwithout being shielded by the gate electrode 602 in case the activationof impurity ions and the like is performed by laser annealing.

[0252] Furthermore, because of the structural advantages, a highlyreliable thin film transistor free from contamination from the substrate601 can be implemented.

EXAMPLE 6

[0253] The material for use in the gate electrodes and the gate lines ofthe thin film transistors described in examples 1 to 5 above is not onlylimited to an aluminum film.

[0254] Other electrically conductive materials, such as Mo, Ti, Ta, Cr,W, etc., can be used for the gate electrode. Furthermore, it is possibleto use a crystalline silicon film rendered monoconductive(one-conductive) as the gate electrode.

[0255] In particular, the use of a crystalline silicon film as the gateelectrode is advantageous in that the temperature range for use in theheat treatment in the fabrication process can be taken with increasedmargin, because the heat resistance of the crystalline silicon film iswell comparable to that of the active layer.

[0256] In case of forming a crystalline silicon film which constitutesthe active layer in a reverse stagger structure, or in improving thecrystallinity of the crystalline silicon film, for instance, a gateelectrode with higher thermal resistance is preferred because it can beused without fear of causing diffusion of the gate electrode material,etc.

EXAMPLE 7

[0257] The thin film transistors described in examples 1 to 6 above areformed not only on an insulating surface, but also on an electricallyconductive film or on an interlayer insulating film formed on asemiconductor device.

[0258] For instance, an integrated circuit having a three-dimensionalstructure which constitutes a thin film transistor according to thepresent invention can be formed on an integrated circuit, i.e., an ICformed on a silicon substrate.

[0259] An integrated circuit having the three-dimensional structureabove is advantageous in that a large scale integrated circuit isconstructed while minimizing the dominating area (occupying area),because the semiconductor device is constructed three-dimensionally.This point is of great importance in minimizing device size.

EXAMPLE 8

[0260] In the present example, described is a case of, in performinglaser irradiation, applying auxiliary heating to the region just infront and just at the back of the object region to be scanned by a laserlight.

[0261]FIG. 9 shows a schematically drawn laser device illustrated inFIG. 7, in which the observation point is concentrated to a part. Thus,the symbols used in FIG. 9 stand for the same portions as those shown inFIG. 7, except for the differing portions.

[0262] The irradiated laser 901 processed into a linear beam by theoptical system and incident to the substrate is irradiated to anamorphous silicon film 903 formed on a substrate 902 having an edgedsurface in a direction approximately perpendicular to the substrate.

[0263] The laser light 901 is irradiated to the entire surface of theamorphous silicon film 903 by moving the stage 711 in a direction shownby an arrow 904. This method is extremely useful, because a highproductivity can be achieved.

[0264] The constitution of the present example differs from thatdescribed in example 1 in that, in irradiating a laser 901 to aparticular region (a linear region), the region just in front of theobject region (which is also provided in a linear or a rectangular form)and the region just at the back of the object region (which is alsoprovided in a linear or a rectangular form) are heated by auxiliaryheating devices 905 and 906.

[0265] The auxiliary heating devices 905 and 906 radiates heat by theelectric current supplied by a power source 907 and thereby generatingJoule's heat. The auxiliary heating devices 905 and 906 must be providedas close as possible to the object region that is irradiated by thelaser 901.

[0266] Electric current is supplied to the auxiliary heating devices 905and 906 in such a manner to heat the amorphous silicon film to apredetermined temperature. This temperature must be set as high aspossible, but by taking the heat resistance of the substrate 902 intoconsideration. According to the knowledge of the present inventors, incase of using a glass substrate, for instance, this temperature is setas high as possible but not higher than the deformation temperature ofthe glass substrate.

[0267] Furthermore, in this case, the temperature for heating theamorphous silicon film 903 by means of the auxiliary heating devices 905and 906 is set to be higher by 50 to 100° C. than the heatingtemperature of the heater built-in the substrate support table 710provided to the lower portion of the stage.

[0268] Furthermore, in this constitution, the auxiliary heating devices905 and 906 are equipped with thermocouples and the like to performprecise temperature control, so that the fluctuation in temperaturedistribution may fall within ±3° C. (preferably ±1° C.) of the standardvalue. Because the temperature control casts considerable influence onthe process of crystallization, this must be effected with great care.

[0269] When laser light 901 is irradiated, the region of the amorphoussilicon film 903 irradiated by the laser light 901 is molteninstantaneously, but because the region surrounding the irradiatedregion is also heated by the auxiliary heating devices 905 and 906, alonger time duration can be taken for the solidification afterirradiating the laser light 901.

[0270] Thus, because the irradiation of the laser light 901 is graduallyeffected while scanning, and therefore an abrupt phase change can beprevented from occurring, the stress inside the film can be relaxed.This enables formation of a highly uniform crystalline silicon film onthe surface of the substrate.

EXAMPLE 9

[0271] The present example refers to a case in which the auxiliaryheating devices 905 and 906 described in the constitution of example 8are provided by means of lamp heating using infrared radiation. FIG. 10shows schematically the laser irradiation device for use in the presentexample. Because the basic constitution is the same as that illustratedin FIG. 9, the same symbols are used for the description.

[0272] In the present example, an infrared ray is irradiated fromhalogen lamps 11 and 12 to the regions in front and at the back of theregion that is irradiated by scanning laser light 901. Because infraredray is hardly absorbed by a glass substrate, while is readily absorbedby a silicon film, the silicon film (amorphous silicon film 903 in thiscase) can be heated selectively.

[0273] The heating method using the infrared-ray-emitting lamps enablesheating the amorphous silicon film 903 alone to a temperature of about1,000° C. (surface temperature) even in case a glass substrate having arelatively low heat resistance is used as the substrate 902.

[0274] However, since peeling off or cracks generate due to thedifference in thermal expansion coefficient between the glass substrateand the silicon film, optimum heating conditions must be obtainedexperimentally. In general, heating using infrared-ray-emitting lamps 11and 12 is performed in such a manner that a surface temperature in arange of from 700 to 900° C. is achieved on the amorphous silicon film903.

[0275] Similar to the constitution described in example 7, an abruptphase change can be prevented from occurring by using the constitutionof the present example. Thus, the stress inside the film can be relaxed,and this enables the formation of a highly uniform crystalline siliconfilm on the surface of the substrate.

EXAMPLE 10

[0276] The present example refers to a constitution similar to thatdescribed in example 1, except for using lamp annealing as a means ofheating the object substrate 709 in irradiating laser.

[0277] That is, referring to FIG. 7, a light source emitting an intenselight is provided inside the substrate support table 710 in the place ofthe built-in heater, and the object substrate 709 is heated by the thusirradiated intense light.

[0278] As the light source above, usable are lamp light sources emittinginfrared or ultraviolet rays. This heating means using light irradiationfrom lamps is highly effective in that the temperature is elevated andlowered at a high rate and a highly uniform annealing effect isobtained.

[0279] The fact that the temperature is increased and decreased at ahigh speed also signifies a considerable increase in throughput.Accordingly, this is also very effective from the viewpoint ofproductivity.

[0280] However, in case of irradiating infrared ray by using a lamp, itis necessary to use a stage 711 made of a glass covered by an SiC or Sicoating, or such made of a quartz substrate, which readily absorbsinfrared ray.

[0281] Furthermore, as a matter of course, the substrate temperaturemust be monitored by providing a thermocouple and the like to the stage711, and the measured results are fed back to control the intensity ofthe intense light radiated from the lamp light source.

[0282] As described above, by employing a constitution as such tocontrol the substrate temperature by using lamp annealing, which issuperior in controllability and uniformity, a laser annealing processfurther improved in uniformity and reproducibility can be implemented.

EXAMPLE 11

[0283] The present example refers to a constitution of an optical systemof a laser irradiation device shown in FIG. 7. FIG. 12 is referred tofor the description. In FIG. 12, the laser light emitted from agenerator (not shown) is incident to a homogenizer 21. The homogenizer21 has functions of correcting the density distribution of theirradiation energy in the width direction of the laser beam which isfinally shaped into a linear laser beam.

[0284] Reference numerals 22 and 23 denote homogenizers which havefunctions of correcting the distribution of the density of radiationenergy in the longitudinal direction of laser beam finally linearlyshaped.

[0285] The laser having an irradiation energy thus controlled by thehomogenizers 21, 22, 23, and 24 is incident to a lens system comprisinglenses 25, 26, and 27. In the lens system, the linear beam is firstshaped in the longitudinal direction by the lens 25. That is, the laseris extended in the lens 25.

[0286] In lenses 26 and 27, the linear laser light is shaped in thewidth direction. That is, the laser light is converged. A mirror 28 isprovided to change the traveling direction of the laser.

[0287] The laser whose traveling direction is changed by the mirror 28is then incident to a lens 29. The lens 29 is provided also to shape thelinear beam in the width direction. The laser transmitted through thelens 29 is irradiated to the object plane 30 as a linear laser beam.

[0288] The object surface 30 corresponds to, for example, a surface ofan amorphous silicon film or a surface of a crystalline silicon filmwhose crystallinity is to be further ameliorated. In the constitutionshown in the present example again, the matter of concern is toconstrain the fluctuation in the irradiation energy density of theirradiated laser per pulse in a range as shown in FIG. 1.

EXAMPLE 12

[0289] The present example refers to a constitution in which theuniformity of the irradiation energy density in the longitudinaldirection of the linear laser beam is ameliorated. FIG. 13 showsschematically the optical system of the laser irradiation deviceaccording to the present example.

[0290] Referring to FIG. 13, the device comprises an optical systemsimilar to that shown in FIG. 8, but which is further improved. Morespecifically, the number of the homogenizers is differed incorrespondence with the anisotropy of the beam shape. In FIG. 13, theportions that are the same as those in FIG. 8 are indicated with thesame symbols used in FIG. 8.

[0291] More specifically, two homogenizers 804 and 31 are provided inthe longitudinal direction of the linear laser, i.e., in the directionin which a higher uniformity is required for the density of theirradiation energy. In contrast to this, only one homogenizer 803, whichcorrects the irradiation energy density in the width direction of thelinear laser, is provided in the width direction of the linear laser,because less uniformity in the irradiation energy density is required inthis direction.

[0292] In a linear laser light, in general, the irradiation energydensity distribution in the longitudinal direction of the beam isconsidered important. On the other hand, the density distribution in thewidth direction of a linear laser is not considered a problem becausethe width is confined within several millimeters.

[0293] Thus, as described in the present example, it is useful toincrease the number of the homogenizers which correct the irradiationenergy density in the longitudinal direction of a linear laser, therebyfurther increasing the uniformity in the distribution of the irradiationenergy density.

[0294] The constitution according to the present invention is highlyeffective in implementing, in a high reproducibility, a further uniformannealing of a large area thin film semiconductor in using apulse-emitting linear laser.

[0295] For instance, in the fabrication of an active matrix displaydevice, the problems attributed to the fluctuation in the laserannealing effect using an excimer laser can be overcome. Morespecifically, the stripe patterns which were considered problematic indisplaying an image can be ameliorated, thereby realizing a liquidcrystal display device having a high image quality.

[0296] Furthermore, the invention disclosed herein is applicable notonly to an active matrix liquid crystal display device, but also toactive matrix-type EL display devices and other flat panel displaydevices.

[0297] While the invention has been described in detail, it should beunderstood that the present invention is not to be construed as beinglimited thereto, and that any modifications can be made withoutdeparting from the scope of claims.

What is claimed is:
 1. A laser-irradiation method comprising annealing asemiconductor film by irradiating a pulse-emitting linear laser light,wherein irradiation energy of the laser light per pulse of theirradiation is distributed within a range of approximately ±3%.
 2. Amethod according to claim 1, wherein the irradiation energy of the laserlight per pulse of the irradiation is distributed within a range ofapproximately ±2%.
 3. A method according to claim 1, wherein the laserlight is irradiated for crystallizing the semiconductor film or forimproving crystallinity of the semiconductor film.
 4. Alaser-irradiation method comprising annealing a semiconductor film byirradiating a pulse-emitting linear laser light, wherein fluctuation inthe irradiation energy with passage of time of the laser lightirradiation is distributed within a range of approximately ±3%.
 5. Amethod according to claim 4, wherein the fluctuation in the irradiationenergy with the passage of time of the laser light irradiation isdistributed within a range of approximately ±2%.
 6. A laser-irradiationdevice for irradiating a pulse-emitting laser light while scanning alinear beam into which the emitted light is processed, whereinirradiation energy of the laser light per pulse of the irradiation isdistributed within a range of approximately ±3%.
 7. A device accordingto claim 6, wherein the irradiation energy of the emitted light perpulse is distributed within approximately ±2%.
 8. A laser-irradiationdevice for irradiating a pulse-emitting laser light while scanning alinear beam into which the emitted light is processed, whereinfluctuation in irradiation energy with passage of time of the laserlight irradiation is distributed within approximately ±3%.
 9. A deviceaccording to claim 8, wherein the fluctuation in irradiation energy withthe passage of time of the laser light irradiation is distributed withinapproximately ±2%.
 10. A laser-irradiation method which comprises aprocess for fabricating a semiconductor device, comprising: a first stepof forming a thin film amorphous semiconductor on a substrate having aninsulating surface; a second step of modifying the thin film amorphoussemiconductor into a crystalline thin film semiconductor by irradiatinga linear light from a pulse-emitting laser and/or by applying a heattreatment; a third step of implanting an impurity element which impartsa one conductive type to the crystalline thin film semiconductor; and afourth step of activating the impurity element by irradiating a laserlight and/or by applying a heat treatment; wherein a peak value, a peakwidth at half height, and a threshold width of a laser energy of thelaser light in the second and the fourth steps above are eachdistributed within a range of approximately ±3% of a standard value. 11.A method according to claim 10, wherein the thin film semiconductor is asilicon film.
 12. A method according to claim 10, wherein the peakvalue, the peak width at half height, and the threshold width of thelaser energy are each distributed within a range of approximately ±1.5%of the standard value.
 13. A method according to claim 10, wherein filmthickness of the amorphous semiconductor film on the surface of thesubstrate is distributed within a range of approximately ±5% of astandard value.
 14. A method according to claim 10, wherein theamorphous semiconductor film is formed by low pressure thermal CVD, andtemperature within the surface of the substrate in forming the film onthe surface of the substrate is distributed within a range ofapproximately ±1° C. of a standard value.
 15. A method according toclaim 10, wherein the irradiation of the laser light is performed underan atmosphere containing helium, and concentration of an impuritycontaining C (carbon) or N (nitrogen) element as a component thereof is1 ppm or lower in the atmosphere.
 16. A method according to claim 10,wherein temperature within the surface of the substrate in irradiating alaser light is distributed within a range of approximately ±5° C. of astandard value.
 17. A method according to claim 10, wherein inirradiating a laser light, an auxiliary heating is applied to a regionjust before or just after the irradiation of the laser light, andtemperature within the region is distributed within a range ofapproximately ±3° C. of a standard value.
 18. A method according toclaim 10, wherein the heat treatment in the second and the fourth stepsare effected as such that temperature within the surface of thesubstrate is distributed within a range of approximately ±5° C. of astandard value.
 19. A method according to claim 10, wherein,concentration of C and N elements in the vicinity of an interface of thecrystalline semiconductor film is 2×10¹⁹ cm⁻³ or lower, andconcentration of C and N elements in a bulk of the crystallinesemiconductor film is 5×10¹⁸ cm⁻³ or lower.
 20. A method according toclaim 10, wherein, the irradiation of the laser light is performedduring duration of irradiation intermittently for a plurality of timesper unit area of the surface to be irradiated, where the duration ofirradiation is expressed by cumulative threshold width of the lightemitted from the laser.
 21. A laser-irradiation device for irradiating alaser light to a thin film semiconductor provided on a substrate havingan insulating surface, comprising: means for emitting the laser light; agas processor connected to the means for emitting the laser light; acontrol unit for controlling an output of the laser light by detecting apart of the light emitted from laser and then feeding back the detectedresult to the means for emitting the laser light; optical system meanswhich shape the laser light into a linear beam; and means for heatingthe thin film semiconductor; wherein, a peak value, a peak width at halfheight, and a threshold width of a laser energy of the laser light areeach distributed within a range of approximately ±3% of a standardvalue.
 22. A device according to claim 21, wherein the thin filmsemiconductor is a silicon film.
 23. A device according to claim 21,wherein the means for heating the thin film semiconductor is heating byusing a heater or a lamp, and the heat treatment by using said means isperformed as such that a temperature distribution within the surface ofthe substrate is within a range of approximately ±5° C. of a standardvalue.
 24. A laser-irradiation device for irradiating a laser light to athin film semiconductor provided on a substrate having an insulatingsurface, comprising: means for emitting the laser light; a gas processorconnected to the means for emitting the laser light; a control unit forcontrolling an output of the laser by detecting a part of the emittedlight and then feeding back the detected result to the means foremitting the laser light; optical system means for shaping the laserlight into a linear beam; means for heating the thin film'semiconductor;and an auxiliary heating device provided in addition to the means forheating the thin film semiconductor, wherein, a peak value, a peak widthat half height, and a threshold width of a laser energy of the laserlight are each distributed within a range of approximately ±3% of astandard value.
 25. A device according to claim 24, wherein the thinfilm semiconductor is a silicon film.
 26. A device according to claim24, wherein the means for heating the thin film semiconductor is heatingby using a heater or a lamp, and the heat treatment by using said meansis performed as such that a temperature distribution within the surfaceof the substrate is within a range of approximately ±5° C. of a standardvalue.
 27. A device according to claim 24, wherein the auxiliary heatingdevice is a heater or a lamp light source, and heat treatment by usingsaid auxiliary heating device is performed as such that a temperaturedistribution within a surface being subjected to the heat treatment byusing said auxiliary heating device is within a range of approximately±3° C. of a standard value.